A general underpants type disposable diaper includes front and back body parts that are joined at both sides to form joined sections at both sides, an outer sheet with a waist opening and a pair of right and left leg openings, and an absorber that is fixed to an inner surface of the outer sheet along a central portion in the width direction in an area ranging from a ventral side through a crotch portion to a back side. Such an underpants type disposable diaper is attached to a wearer by inserting the legs of the wearer through the waist opening into the leg openings.
Other than such a diaper with a single-piece outer sheet, there has been proposed a two-separated type disposable diaper which has two separate ventral- and back-side outer sheets, the ventral- and back-side outer sheets being not connected but separated at the crotch portion (refer to Patent Document 1, for example). The two-separated disposable diaper has advantages that, at the time of manufacture, trims (unnecessary waste portions) can be reduced in punching out the leg openings, and materials for the ventral- and back-side outer sheets can be separately selected.
Meanwhile, an absorber in the two-separated disposable diaper includes a liquid pervious top sheet on a top side, a liquid impervious sheet on an underside, and an absorbent element interposed between the foregoing sheets to absorb and retain a liquid. The absorber is connected on the under surface at a front end portion to the ventral-side outer sheet on the inner surface at a central portion in the width direction, and is connected on the under surface at a back end portion to the back-side outer sheet on the inner surface at a central portion in the width direction. The absorber is exposed to outside at an intermediate portion between the front and back end portions through a separation area between the ventral- and back-side outer sheets at the crotch portion. If the liquid impervious sheet is not covered on the under surface, the liquid impervious sheet is exposed between the ventral- and back-side outer sheets. Since the liquid impervious sheet is different in appearance and texture from the ventral- and back-side outer sheets, the liquid impervious sheet is preferably covered with a nonwoven fabric not so as to be exposed, as described in Patent Document 1.    Patent Document 1: JP 2005-027839 A